1362 Agonistic 4–1BB IgM antibodies enhance CD8+ T cell proliferation and proinflammatory cytokine secretion in vitro and in vivo by Adam Smith, Umesh Muchhal, Dean Ng, Poonam Yakkundi, Gary Bolton, Yuan Cao, Tasnim Kothambawala, Beatrice Wang, Deepal Pandya, Vidhya Bai Krishnoji Rao, Elizabeth Perez, Paul Hinton, Hyewon Phee, Sachi Rahman, Thin Wai, Natalia L dos Santos, Aditya Bharti, Balaji Banoth, Harrison Horwitz, Bruce A Keyt, Angus M Sinclair